The present invention relates to a doctor blade apparatus for coating apparatus and particularly to a doctor blade apparatus establishing improved filling of a coating roll and stablizing the flow of liquid in the supply.
In the application of a ink coating to a member, rotary coating applicators are widely used. Coating is used herein to broadly define any liquid transfer from a supply. In a practical system, a gravure or analox cylinder or roll is rotatably mounted within the upper surface of the coating material to be transfered to the web. The surface of the roll is formed with minute recesses or cells to carry the coating material. The coating is accurately applied to the cylinder by mounting of a doctor blade to the discharge side of the bath. The roll dips into the material with pressure filling of the cells and the doctor blade removes excess material from the surface of the cylinder such that a precise and uniform quantity of the material is applied into the cells. The coated surface in then moved onto the moving web, directly or through an offset cylinder for subsequent transfer to the web, in accordance with known and recognized roller applicators.
In such apparatus, the high speed rotation of the cylinder in the bath tends to establish a flow of the material within the bath. The material tends to flow to the downstream side of the cylinder, with creation of a static pressure. The liquid material rises in the downstream side and tends to circulate about the ends of the cylinder to the upstream side with a disturbance in pressure for the filling the cells. Further, undesirable agitation and foaming of the material within the bath is often created. As the speed of rotation increases, the art has taught the use of special packing rolls for filling of the cells.